1. Field of the Invention
This invention relates to a curing agent and a coating composition, more specifically to a curing agent containing blocked isocyanate compounds and a cationic electrodeposition coating composition which contains it.
2. The Prior Art
A standard cationic electrodeposition coating composition contains a base resin and a curing agent. The curing agent used in such a coating composition is generally a blocked isocyanate compound.
FIG. 1 shows the relationship between the temperature of the electrodeposition bath and the film thickness in cationic electrodeposition painting. It is shown that, as the bath temperature rises, the film thickness first decreases and then increases. The temperature of the electrodeposition bath at which the film thickness is at a minimum is called "the minimum film -formation temperature (MFT)". Electrodeposition coating is conducted around this MFT. With conventional cationic electrodeposition paint which contains the curing agent as described above, the film thickness is significantly influenced by changes in the temperature of the electrodeposition bath around MFT, and therefore it is necessary to keep the temperature of the electrodeposition bath constant in order to obtain a constant film thickness.